The device of the instant invention relates to fixtures for dipping electronic circuit boards into a tank of a clear liquid protective coating to waterproof the circuit board. Specifically, it is desirable not to coat certain parts of or on a circuit board; for example, edge pins that are designed to allow the board to be plugged into another component.
In the past circuit boards have been dipped in this coating while oriented so that they are hanging down vertically from the workpiece holder bars normally used. This requires parts of the circuit board that are not to be dipped to be covered with a masking substance. The masking substance prevents the coating material into which the circuit boards are dipped from adhering to such things as electrical connections at the edges of circuit boards, pins for plugs, and the like. This is a very time consuming step, and the masking must be removed after the dipping and the curing of the coating are achieved. By means of a unique and simple design my invention eliminates the need for masking and demasking steps, yet allows very precise control over the boundary between dipped and undipped parts. The circuit board is designed to optimize dipping with the device of this invention.
Nowhere does the prior art reveal the unique and simple design of my invention for avoiding the necessity of masking a circuit board. U.S. Pat. No. 4,794,018 (Scheetz) shows an apparatus and method to avoid coating undesired areas on a P.C. Board. However, the structure of the apparatus and the method are completely different from my apparatus and method. Scheetz does disclose the use of a drain edge which functions like a weir but does not reveal anything else that is even similar to the structure of my invention. U.S. Pat. No. 2,964,007 (Buffington) discloses a "Dip Soldering Machine" for soldering circuit boards. Buffington merely shows that the level of solder in the tank is controlled by a float switch incapable of the close control required here. The function and structure of this machine are completely different from that of my invention. My invention relates to the use of protective coating materials and not solder. Buffington is designed to solder components to a printed circuit and requires the use of a stainless steel template 82 to achieve soldering in the proper manner. U.S. Pat. No. 3,566,891 (Koch) shows a conveyor system with an adjustable pool. Koch is designed for and teaches "a tank arrangement particularly adapted for processing small parts characterized by the indexing of several tanks into processing positions through simultaneous vertical movement". (Abstract of Koch patent.) Koch does not show the structure or the advantage of my invention. U.S. Pat. No. 3,956,540 (Laliberte et al) shows a structure in which the level of material within the tank is controlled by means of electric eye beams. (Col. 5, lines 66+ .) This structure functions by raising and lowering the dip tank containing the coating solution. The purpose of Laliberte is to cover an object with a coating of a predetermined thickness. The idea is to coat an entire workpiece, like an optical lens, with the desired type of coating. Col. 1, lines 64-67. Nowhere does Laliberte teach or even suggest the desirability of the structure or function of my invention for coating only a desired part of a circuit board. U.S. Pat. No. 4,597,931 (Watanabe et al) discloses a method for manufacturing a windshield having a coating of varying thickness. Essentially, a base windshield is suspended over a dipping tank 23 containing a silicone coating solution 24. The tank 23 is raised and lowered in a manner designed to vary the thickness of the coating on the base windshield. The coating does not terminate at a precise edge. This structure neither teaches nor reveals my invention. Finally, U.S. Pat. No. 4,840,821 (Miyazaki et al) merely discloses an apparatus and method for forming an LB film on a substrate in which the film is deposited by raising and lowering the surface of the liquid on which a group of molecules is spread relative to the substrate. This does not teach my invention. The main difference between my invention and the prior art is that the circuit boards are mounted on the fixture in a position such that the plane of the circuit board is horizontal or substantially horizontal. With the other elements for precise control of the level of the liquid coating, this achieves a precision of location of the coating edge that allows parts to be located on the high edge of the circuit board, or projecting upwardly, where coating will not occur.
It is the objective of my invention to eliminate the need for using a masking substance when dipping a circuit board.
It is a further objective of my invention to be able to control the depth to which the circuit board is dipped to about 0.015 inches or approximately 0.38 millimeters (mm).
It is a further objective of my invention to dip circuit boards in a generally horizontal rather than vertical orientation.
It is a further objective of my invention to allow for a quick change of tooling thus improving the speed and efficiency of the manufacturing process.